hi all
when i get up to 70mph the genlight comes on. would that be a loose belt or something internal. im also after a second hand mirror as all my chrome is well aged and a bit pited. i need one on the passenger side as trying to pullout in traffic is hard when you are on the wrong side in australia.
thanks eddy

Ian, I will assume your generator brushes are good. If you're not sure, give them a check. New generator brushes are cheap.

It's important you understand how the GEN light works.
On one end, the bulb is fed from your key switch (positive).
On the other end, it's fed from your generator (also positive).

So, now we can measure the difference between your battery voltage and your generator's output voltage.

When you first turn the key on before starting the engine, your GEN light shines because the generator is putting out nothing but the battery has 12-volts.

If you throw a belt, your GEN light shines, for the same reason.

If you have your accessories on and stopped at a light, your GEN light might flicker because the gen is putting out very little at idle speed but the battery is at 12-volts.

Ok, I led you around the barn. Now the real answer. You may have a voltage regulator that is bad. The voltage regulator supplies field voltage to the generator so the gen can produce power. Without field, the gen puts out nothing. Without a belt, the gen puts out nothing. Even still, that important GEN light draws a comparison to tell you if your system is charging or not.

ALWAYS make sure your GEN light works. If you turn the key and it doesn't shine, buy a new bulb (I think it's a #57).

How do you know when the battery is charging? Put a voltmeter across the battery terminals and look for 13.5-volts or more when the engine is above idle speed.

To prove your generator can produce, jumper the BATT and FLD terminals on your voltage regulator and watch the voltmeter on your battery climb. Don't leave the jumper on for long because you are bypassing all voltage regulation. I use one minute intervals.

When the generator is charging, you can hear the engine speed go down and sometimes you can hear the generator as it produces power. Hope this helps. - Dave

Yes, and if you converted to an alternator you'll see the Gen light glow. It glows brighter when you add headlamps, blower, radio, and stoplights-especially at idle. I'm surprised at how hard the alternator works trying to charge the battery. My belt will squeal after sitting at a stop light for a while with the voltage demand increased. (A bit embarrassing, but one alternator expert says 'tighten the belt'!)

Dave , I have to disagree on how to test generator / regulator output.

"B" circuit generator / regulator (original Thunderbird).
You NEVER want to jump battery terminal to field terminal at the regulator with the wires attached to the regulator. This will burn out your voltage regulator field contact system in your regulator.

Testing your generator / regulator for output :
Remove field wire from voltage regulator and with engine running at 1200 to 1500 rpms. Touch the field wire to armature terminal at regulator for a few seconds. If the voltage increases to 14 to 15 volts. The voltage regulator is bad. No change in voltage the generator is bad or wiring issues. This test is unregulated so do not run for more than a few seconds to read your volt meter.

Dave , I have to disagree on how to test generator / regulator output.

"B" circuit generator / regulator (original Thunderbird).
You NEVER want to jump battery terminal to field terminal at the regulator with the wires attached to the regulator. This will burn out your voltage regulator field contact system in your regulator.

Testing your generator / regulator for output :
Remove field wire from voltage regulator and with engine running at 1200 to 1500 rpms. Touch the field wire to armature terminal at regulator for a few seconds. If the voltage increases to 14 to 15 volts. The voltage regulator is bad. No change in voltage the generator is bad or wiring issues. This test is unregulated so do not run for more than a few seconds to read your volt meter.

Mike, your suggestion is plausible BUT it doesn't get the job done.
Mike, study the wiring diagram and notice that the armature and field are already connected via both normally closed contacts. If you go through your procedure, nothing has changed.

I'm trying to determine if the generator is capable of outputting charging current.

Since I suggest adding a temporary jumper from +12 to the field with the engine running, there is nothing that can be harmed. Remember, during normal operation the generator's armature outputs 30-amps at ~14-volts. All that is impressed upon the field until either (voltage or current) relay contacts open.

ALSO, the GEN light is already connected to the armature (and field coils) as soon as the key is turned 'on' through both the regulator's N.C. contacts. This 'tickles' the armature and makes enough magnetism (in the correct direction) to start producing current when the armature windings pass through the field magnetism. There should be NO reason to 'flash' or 'polarize' a charging system with a GEN light. Case in point: How many Squarebird owners had to polarize, even after 50 years?

DeanJ, you should have a resistor across your GEN light wires for two reasons; to shunt that small amount of current that makes your light flicker but more importantly... If your GEN light burns out, the alternator will not know the key is on and it will stop charging. The resistor will pass enough power by itself to keep the alternator going. Even with the resistor, your GEN light should work as you would expect. - Dave

DeanJ, you should have a resistor across your GEN light wires for two reasons; to shunt that small amount of current that makes your light flicker but more importantly... If your GEN light burns out, the alternator will not know the key is on and it will stop charging. The resistor will pass enough power by itself to keep the alternator going. Even with the resistor, your GEN light should work as you would expect. - Dave

Dave, I wouldn't know what resister to use. I take it a good spot for this might be the engine compartment close to the alternator since anything under the dash is a pain.

Again, the reason is just to keep the GEN light from burning out prematurely and the alternator functions normal?

Dean, sometimes I assume too much. this time I assumed you had the wiring diagram for your conversion.

Here it is:
Notice the resistor in the top blue box. Use a 1/2-watt, 560-ohm resistor. Any radio shop will have one. The resistor simply connects across the light bulb socket. You cannot stop a bulb from burning out so the resistor keeps your charging system going whether the bulb burns out or not. It also shunts a small amount of current which stops that flickering.

These old starter motors and generators use brushes. To be more specific, ALL charging current goes through those brushes (unlike alternators). They do not last as long as modern alternators. The same holds true for starter motors, all current goes through the brushes. Rockauto.com sells brushes for $6-7. They are relatively easy to change. Ford provided inspection covers to show what's really going on.

It always puzzled me, why people let their starters and generators go until catastrophic failure when preventive maintenance is not only cheap but available. In The States, these original starters and generators aren't always available. When that happens, the prices soar.

If you're lucky enough to get an early warning, don't wait until failure catches you far from home. - Dave

personally I would never put a resister in parallel with the charge light. The charge light is the first port of call on your charging systems health. If you "gen" light didn't come on when turning your ignition on it should be investigation straight away and the assumption shouldn't be made that the globe is just blown the resister will keep things working because 9 out of 10 times it won't be the globe, it will be a charging system fault.

On most alternators the alternator warning light provides excitation by having ignition on one side of the globe, that power passes through the globe down to the D+ wire on your alternator which in turn connects to your rotor positive brush, that signal then goes through your rotor out the negative brush through the regulator then to earth turning the light on and providing a slight magnetic field for initial charging. This in turn informs you if the regulator, brushes, or rotor coil are functioning correctly, any fault that will not allow the light to turn on.

Driving, racing or working on cars can be hazardous. The procedures and advice on this website including the message board are opinion only. Squarebirds.org and its webmasters and contributors do not guarantee the correctness of the advice and procedures. The Squarebirds.org and its webmasters assume no liability for any damage, fines, punishment, injury or death resulting from following these procedures or advice. If you do not have the skills or tools to repair your car, please consult a professional. By using this site you agree to hold harmless the Squarebirds.org, its authors and its webmasters from any resulting claim and costs that may occur from using the information found on this site.

Any submissions to this site and any post on this site becomes property of Squarebirds.org . The webmasters reserve the right to edit and modify any submissions to this site. All material on this is site is copyrighted by the Squarebirds.org. Reproduction by any means other than for personal use is strictly prohibited. Permission to use material on this site can be obtained by contacting the webmasters. Copyright 2002-2016 by Squarebirds.org.